A folded bill, as a kind of a non-circulating bill, is not suitable for circulation any more. Therefore, when a folded bill is inputted into a recognition device, the recognition device needs to recognize and classify it as a non-circulating bill.
Limited to factors such as a conventional imaging device, illumination variations, imaging environments, signals obtained by a signal collecting module of a self-service device is not robust enough, which make a characteristic in the signal of a folded bill insignificant, resulting in difficulties in recognizing a folded bill.
Characteristic description is a key premise of the folded bill recognition. Based on a currently used signal, if only a single-characteristic description method, such as a conventional approach of calculating simply a gray mean value or an approach of performing binaryzation on an image with a threshold and counting abnormal pixels, is adopted, it is difficult to distinguish the folded bills from interfered or fouled bills. The main reason that the conventional characteristic description cannot lead to a good effect is that the folded bills and the interfered or fouled bills are not effectively distinguished or pre-processed.